1. Field of the Invention
This invention relates to concrete screeds of a type providing plural screed surfaces.
2. Description of the Related Art
Applicant's prior U.S. Pat. No. 4,030,873 discloses a portable screed incorporating a motor-driven vibrating shaft within a lightweight open structural frame. A winching mechanism for a vibrating shaft type screed is described in applicant's prior U.S. Pat. No. 4,253,778.
Another type of screed employs a roller which is rotated in a direction opposite to the direction of travel and screeds the concrete by moving the roller over freshly poured concrete in front of the roller. One such motor-driven screed roller is the Razor Back Roller Finisher sold by Allen Engineering Corporation of Paragould, Ariz. A similar type of roller screed identified as the Hurricane screed is sold by C & S Manufacturing Company of Tulsa, Okla.
The roller type screed has a number of advantages particularly in application to screeding concrete on slopes and grades, but has the disadvantage of not consolidating concrete as effectively as does a vibrating frame type screed. In addition, when roller screeds are provided in extended lengths, above about 25 feet, deflection of the roller element is encountered, which adversely affects the profile of the concrete being screeded in many applications, or alternatively requires the fabrication of the roller element with a thick-walled structure to resist the deflection.
In an attempt to overcome the deficiencies of the roller type screeds while realizing the benefits associated with vibrating frame type screeds, applicant's copending U.S. patent application Ser. No. 936,480 filed Nov. 26, 1986, and entitled "Multi-Section Screed Roller Apparatus", proposes an improved screed comprising an open multi-section frame on the front of which is mounted a motor-driven multi-section screed roller, and behind which is provided a pair of screed plates. On the rear of this screed is provided a driven vibrating shaft which extends lengthwise of the screed to induce vibrations primarily in the trailing portions of the screed for consolidation of the concrete after it has been roughly screeded and graded by the multi-section roller. This apparatus further includes means for winching the screed in the direction of travel, and incorporates a turnbuckle arrangement compensating for any tendency of the multi-section roller to deflect when the screed length is relatively long.
While the screed roller apparatus of the aforementioned Ser. No. 936,480 application incorporates a number of advantageous features of roller screeds and vibrating frame type screeds, in applications where very wet concrete is being screeded, the rough screeding, grading and distributing functions of the roller are not fully optimally achieved.
Accordingly, there exists a continuing need for an improved screed apparatus utilizing auxiliary means for preliminary rough screeding, grading and distributing of the concrete prior to final screeding and consolidation by the apparatus.
It is therefore an object of the present invention to provide an improved screeding apparatus of the aforementioned type, which provides a high degree of screeding efficiency, including concrete distribution and consolidation prior to final, i.e., finishing, screeding action.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.